<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <button id="btn">点击</button>

    <script>
        //事件句柄
        btn.onclick = function() {
            console.log(1)
        }
        btn.onclick = null;
        // function f1() {
        //     console.log(1)
        // }
        // btn.addEventListener("click", f1)
        // btn.removeEventListener("click", f1)
    </script>
</body>

</html>